1. Field of the Invention
The present invention relates generally to semiconductor devices, and more particularly to a semiconductor switching device.
2. Description of the Related Art
Conventional switching devices such as FET switches, diodes or Gilbert Cells are capable of providing switching capability for electrical signals. Such switching devices provide a differential output based upon a differential gate signal applied to an input current.
For example, as is well known, a Gilbert Cell single-balanced mixer includes an RF signal input carrier in electrical communication with the respective sources of first and second transistors. The gate of the first transistor is connected to a high potential voltage connection (LO+) and the gate of the second transistor is connected to a low potential voltage connection (LO−). The drain of the first transistor is in electrical communication with a high current output (IF+) and the drain of the second transistor is in electrical communication with a low current output (IF−).
In operation, a first voltage applied to LO+ and a second voltage applied to LO−, which is the complement of the first voltage, results in current flow through IF+ and little or no current flow through IF−. Reversing the voltage applied to LO+ and LO− reverses the current flow through IF+, and IF−, respectively.
A Gilbert Cell double-balanced mixer with two single-balanced mixers includes two RF signal input carriers, a high input current (RF+) and a low input current (RF−) that is the complement of RF+. A first voltage (LO+) is applied to the gates of first and fourth transistors. A second voltage (LO−) that is the complement of the first voltage is applied to the gates of the second and third transistors. The drains of the first and third transistors are in electrical communication with IF+, and the drains of the second and fourth transistors are in electrical communication with IF−.
In operation, a first high voltage applied to LO+ and a second low voltage applied to LO− results in current flow through IF+ and little or no current flow through IF−. Reversing the voltage applied to LO+ and LO− reverses the current flow through IF+ and IF−, respectively.
However, during operation of the single-balanced or double-balanced Gilbert Cell the gate of one transistor normally turns on either slightly ahead of, or behind, the instant that another gate switches off due to slight differences in either the gate characteristics or a drive circuit imbalance. This transient time in which both gates are either on or off contributes to device noise and/or nonlinearity. As the frequency of applied voltages LO+ and LO− increases, the transient time becomes a greater percentage of the voltage period.
In addition, the double-balanced Gilbert cell requires balanced inputs to optimize the distortion performance and LO to IF isolation.